• 한국태양에너지학회 논문집
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• 제35권5호
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• pp.49-56
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• 2015

In this study a hybrid heating system based on geothermal source and solar heat was developed in order to save energy for greenhouse heating and its field performance was evaluated. Developed system are composed of following parts: water tank, heat exchanger, heat pump, fan coil unit and heat storage unit. The working performance test was carried out in a greenhouse cultivating oriental orchids being managed by $23^{\circ}C$. Field performance test results showed that average heating coefficient of performance ($COP_h$) was 3.4 for the period from mid-January to mid-March 2013. Heating coefficient of performance ($COP_h$) of developed hybrid heat pump system was more sensitive to water tank temperature than outside air temperature. This study showed that developed hybrid heat pump system has a potential to save the heating costs up to 91% compared to conventional agricultural oil heaters.

• 대한기계학회논문집B
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• 제20권12호
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• pp.4027-4035
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• 1996

Accuracy of gas flow measurements using sonic nozzle and factors which influence on the discharge coefficients of sonic nozzle are investigated with high pressure gas flow standard measurement system. The gas flow measurement system comprises two compressors, storage tank, temperature control loop, sonic nozzle test section, weighing tank, gyroscopic scale and data acquisition system. The experiments are performed at various nozzle throat diameter and inlet pressure. Overall uncertainty of discharge coefficients is estimated to less than .+-.0.2% and most of experimental data fall into this range. Dependence of discharge coefficients on the Reynolds number is good agreement with those suggested in ISO document. The influence of swirl on the discharge coefficients becomes greater as the nozzle throat diameter is enlarged. The discharge coefficient of conical nozzle shows about 4.5% lower discharge coefficients than those of toroidal nozzle, but variation trend with Reynolds number is very similar each other and reproducibility of data is very good.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.360-367
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• 2003

Diamond-like carbon(DLC) films are considerable research interest because of their widespread applications as protective coatings in areas such as optical windows, magnetic storage disks, car parts, biomedical coatings and as micro-electromechanical devices(MEMs). DLC films were deposited on WC-Co by PECVD using Ar, $C_2H_4$ gas. Tribological tests were conducted using a ball-on-disk type tribometer in dry air. Three kinds of counter-bodies balls were used. The counter-bodies balls are SM45C, SUJ2 and $ZrO_2$(3.17mm in diameter). Wear rate of the samples were calculated after measuring the worn-out volume of the wear track. As results wear test, the higher hardness of counter-bodies, friction coefficient low. As result of XPS estimation, wear debris generated as an oxide lower the friction coefficient.

• 한국농공학회논문집
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• 제50권6호
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• pp.3-12
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• 2008

It is important to estimate accurate effective rainfall to analyse flood flow and long-term runoff for the rational planning, design, and management of water resource. The initial abstraction is also important to estimate effective rainfall. The Soil Conservation Service (SCS) has developed a procedure and it has been most commonly applied to estimate effective rainfall. But the SCS method still has weak points, because of unnatural assumptions such as antecedent moisture conditions and initial abstraction. The coefficient of initial abstraction(K) is depending on the soil moisture condition and antecedent rainfall. The maximum storage capacity of Umax which is calibrated by stream flow data in the proposed watershed was derived from the DAWAST(DAily WAtershed STreamflow) model. The values of K obtained from 69 storm events at the five watersheds are ranging from 0.133 to 0.365 and its mean value is 0.207. Effective rainfall could be estimated more reasonably by introducing new concept of initial abstraction. The equation of $K=0.076Sa^{0.255}$ was recommended instead of 0.2 and it could be applicable to the small-medium rural watersheds.

• 한국자동차공학회논문집
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• 제21권1호
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• pp.23-29
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• 2013

In recent years, development of energy conversion systems using hydrogen as an energy source has been accelerated globally. Even though hydrogen is an environment-friendly energy source, safety and effectiveness issues in storage, transportation, and usage of hydrogen should be clearly resolved in every application. Therefore, sensors for detecting hydrogen leakage, especially for fuel cell electric vehicles, should be designed to have much higher resolution and accuracy in comparison with conventional gas sensors. In this study, we conducted to determine the design parameters for the semiconductor hydrogen sensor with optimized sensing conditions under the thermal distribution characteristic and thermal transfer characteristic. The heat generation study on power supply voltage was studied for correlation analysis of thermal energy according to the power supply voltage variation from 1.0 voltage to 10.0 voltage every 0.5 voltage. And we studied for the temperature coefficient of resistance with hydrogen sensor.

• 물과 미래
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• 제19권4호
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• pp.347-354
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• 1986

강우와 유역특성으로부터 홍수유출을 예측하기 위해서 Nash 모델의 매개변수 N, K가 결정될 필요가 있다. 또한 순간단위도의 매개변수 N,K가 적율법에 의해서 유도되어야 한다. 강우특성으로부터 유도되는 Nash 모델의 매개변수는 낙동강에 위치한 위천유역에 적용하였다. 선형이론에 의한 순간단위도의 유도에 있어서 강우특성으로서 저장상수 K는 매우 높은 상관계수 0.97을 가진 K=1.327 $·$·$·$·$·$을 채택하였다. 이와 같은 강우특성으로서 Gamma 함수 N는 매우 높은 상관계수인 0.97로서 N=0.032$·$·$·$·$·$으로 나타났다. 검정결과 Nash 모델의 순간단위도와 이로 인한 홍수유출은 강우특성으로부터 예측될 수 있음이 입증되었다.

• 산업식품공학
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• 제14권4호
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• pp.354-358
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• 2010

The methods for determining the diffusion parameters for the diffusion of d-limonene, a major volatile compound of orange juice, through a multi-layered food packaging material and predicting its absorption into the packaging material have been investigated. The packaging material used was the 1.5-mm thick multi-layered packaging material composed of high impact polystyrene (HIPS), polyvinylidene chloride (PVDC), and low density polyethylene (LDPE). Orange juice was placed in a cell where volatiles were absorbed in the sample package and kept at $23{\pm}2^{\circ}C$ for 72 hr. The d-limonene absorbed in a 1.5-mm thick multi-layered food packaging material was analyzed by a solid phase micro-extraction (SPME). The absorption parameters for the absorption of d-limonene in the packaging material were determined and absorption of d-limonene into the packaging material was predicted using absorption storage data. The SPME desorption at $60^{\circ}C$ for 1 hr resulted in the most sensitive and reproducible results. The diffusion coefficients of d-limonene in the packaging material and the partition coefficient at $23{\pm}2^{\circ}C$ were approximately $1-2{\times}10^{12}m^2$/s and 0.03, respectively. The absorption profile no earlier than 30 hr was fit well by a model derived from the Fick's law.

• Journal of Power Electronics
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• 제19권5호
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• pp.1270-1277
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• 2019

A problem with virtual synchronous generator (VSG) systems is that they are difficult to operate stably with photovoltaic (PV) power as the DC side. With this problem in mind, a PV-VSG control strategy considering the dynamic characteristics of the DC side is proposed after an in-depth analysis of the dynamic characteristics of photovoltaic power with a parallel energy-storage capacitor. The proposed PV-VSG automatically introduces DC side voltage control for the VSG when the PV enters into an unstable working interval, which avoids the phenomenon where an inverter fails to work due to a DC voltage sag. The stability of the original VSG and the proposed PV-VSG were compared by a root locus analysis. It is found that the stability of the PV-VSG is more sensitive to the inertia coefficient J than the VSG, and that a serious power oscillation may occur. According to this, a new rotor model is designed to make the inertial coefficient automatically change to adapt to the operating state. Experimental results show that the PV-VSG control strategy can achieve stable operation and maximum power output when the PV output power is insufficient.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.172.2-172.2
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• 2010

This study was carried out in order to reduce the installation expense of heating system for greenhouse comparing to geothermal heat pump and develope the coefficient of performance (COP) for a heat pump. For getting plenty of heat flux from geothermal energy. Surface water in river channel was used for getting a lots of geothermal heat by penetrating water through underground soil layer of the river bank that make heat transmission to passing water. The range of water temperature after the process of Ground filtration is 13~18 degrees celsius which is very similar to low heat source of geothermal heat pump system and the plenty amount of heat source from that make the number of geothermal heat exchanging hole and the expense for geothermal heat exchanger construction reduced. Drainage well is also used for returning filtration water to the aquifer that keep the water good recirculation from losing geothermal heat and water resource. For the COP improvement of Heat pump, thermal storage tank with separating insulation plate according to the temperature difference make the COP of Heat pump that is similar to thermal storage tank with diffuser. Developed thermal storage tank make construction expense cheaper than customarily used one's. and that sand filter and oxidation sand (FELOX) are going to be used for improving ground filtration water quality that make heat exchanger efficiency better. All above developed component skill are going to be set on the Ground filtration water source heat pump system and applied for medium, large scale for protected greenhouse in riverside area and on-site experiment is going to do for optimizing the heating system function and overcome the problem happening in the process of on-site application afterward.

• Journal of Biosystems Engineering
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• 제32권3호
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• pp.166-172
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• 2007

Egg quality indices are related with freshness, size of air chamber, loss of weight, and viscosity of the yolk and the protein. However, since the described quality parameters require measured in a destructive way, it is not suitable to inspect the egg quality with complete enumeration. Therefore, this study was performed to investigate the potential of image analysis method for evaluation of internal egg quality. Samples of 90 fresh eggs were collected immediately after laying and stored up to 24 days. Five eggs were randomly drawn from each storage condition (packing vs unpacking) at a regular interval and loss of weight, specific gravity and size of air chamber were measured. The image analysis for nondestructive measurement of size of air chamber was also studied. Results showed that the egg weight and gravity gradually decreased with increasing of storage days, while the size of air chamber linear increased caused by evaporation of water through the shell. A relationship a between conventional method and the image analysis method for measuring the size of air chamber was developed with the correlation coefficient of 0.928. The new finding implied that image analysis might provide a useful nondestructive tool to assess internal egg quality.